In such a kind of clamp mechanisms, it is generally known to press all or a part of an opening of a fitting hole with a head portion and to clamp a tip, by setting the outer diameter of a shaft portion of a clamp member to be smaller than the inner diameter of the fitting hole formed in a tip body, setting the outer diameter of the head portion formed at an end of the shaft portion to be larger than that, forming a screw portion inserted into a tip fitting seat of a tool body at the other end of the shaft portion, positioning the tip body onto the tip fitting seat, and then inserting the clamp member into the fitting hole from the screw portion. However, in the traditional clamp mechanism, since the clamp member should be also detached from the tool body when the tip is detached, the detachment work is troublesome and the detached clamp member may be lost.
In Japanese Unexamined Utility Model Publication No. 1973-12675 (“JP '675”), PCT Japanese Translation Patent Publication No. 2002-512891 (“JP '891”), and U.S. Patent Publication No. 2003/0165362 (“US '362”), there have been suggested clamp mechanisms in which a head portion of a clamp member, disposed in a tool body and can advance and retreat, has a section with a non-circular cross section. The section has a protrusion protruded from the outer circumference of a shaft portion, such as a petal shape, a triangular shape, or a cross shape, but not a circular shape, in which a concave portion through which the protrusion can pass and a convex portion which engages with the protrusion are alternately formed in the circumferential direction on the inner circumference of an opening of a fitting hole. In such clamp mechanisms, at the time of detaching a tip, the clamp member is protruded, and the tip is pulled out by rotating a tip body or a clamp member so as to position the protrusion and the concave portion with respect to each other. On the other hand, at the time of clamping the tip, the head portion is allowed to pass through the fitting hole in a state where the protrusion and the concave portion are positioned with respect to each other, the tip body or the clamp member is rotated so as to position the protrusion and the convex portion with respect to each other, and then the convex portion is pressed and clamped by the protrusion by inserting the clamp member so as to advance the clamp member toward a tip fitting seat.
In Japanese Unexamined Patent Publication No. 1999-19808 (“JP '808”), there has been suggested a clamp mechanism in which a clamp hole portion, through which a shaft portion of a clamp member having a screw portion can pass but a head portion cannot pass, is formed in a tip body; a passing hole, through which the head portion can pass, is formed on at least one side of an opening of the clamp hole; the shaft portion can pass between the clamp hole and the passing hole; the tip body is fitted to the tip fitting seat by allowing the head portion to pass through the passing hole at the time of fitting a tip in a state where a clamp member inserted into the tip fitting seat is not completely detached therefrom but is loosened; the tip body is brought into contact with the wall surface of the tip fitting seat so as to position the tip body and to allow the shaft portion to pass through the clamp hole by allowing the tip body to slide; and then the opening of the clamp hole is pressed with the head portion to clamp the tip by inserting the clamp member in a screw manner.